The Shrimphaus recently spontaneously developed a relatively solid whitish layer on the top surface of the water.  I’m convinced this layer was a biofilm, a macroscopic colony of microscopic organisms holding themselves together.  Although not usually considered dangerous to plants or animals, biofilms don’t look very nice, and can potentially inhibit beneficial gas exchange between the water and the environment if allowed to get out of hand so are probably best prevented/removed.

An airstone can solve  biofilm problems

An easy-to-try cost effective way to remove and prevent biofilm formation is to add an airstone.  Bubbles from the airstone as they break on the water surface will rapidly disrupt and presumably sink biofilm and prevent it from recurring.  For some reason, bubbles breaking on the surface are much more effective at disrupting biofilm than is surface agitation from simple water flow.  A side benefit of the bubbles is greater oxygenation of the water, which may also benefit aquarium residents.  In a CO2 gas injected tank, airstone bubbles can potentially promote the removal of CO2 from the water column, so one approach can be to have the CO2 injection during the day when the plants can use the carbon, switching the CO2 off and turning the airstone on at night.  In ‘low tech’ setups like the Shrimphaus without injected CO2 gas, you can run an airstone continuously.

Aquarium oil slicks may actually be biofilm

Biofilm can very much resemble an oil slick on the surface of an aquarium.  A key difference is a biofilm can create (and recreate) itself without needing a ’cause’, whereas an oil slick is caused by something changing, such as if oil were released from dead fish, or from release of contaminating oil on your hands.  If your aquarium surface was clear and then suddenly over a day or two develops a surface layer all on its own, that’s probably a biofilm.  Both an oil slick and a biofilm are easily, if messily, removed using paper towels draped on the water surface then scooped out and discarded.  The biofilm, however, will reform in a day or two whereas a one-off oil spill will not, so if you find yourself repeatedly going after the ‘oil’ with paper towels, the reason why it keeps coming back is because it is a biofilm and is growing back.

Shrimphaus airstone

The Shrimphaus uses a Nexberg mini piezo air pump.  The complete setup include airstone, tubing, water check valve and LED thermometer strip came in under £20.  I’m super happy with the pump – it’s easily powerful enough and really quiet.  I swapped out the airstone it came with for an Oase biOrb air stone which gives slightly smaller bubbles and seems a little quieter.  The Shrimphaus is at ambient room temperature so no need for the thermometer.

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